Sclerotinia White Mold in Soybeans

Conditions that usually create a white mold year are temperatures below 85°F and above average precipitation or high humidity around the time of flowering. With most of the region already experiencing these weather conditions and most of the soybean crop is entering the flowering stage, this raises concerns for white mold risk this year.

The white mold fungus, Sclerotinia sclerotiorum, primarily infects the soybeans through senescing flowers around the R1-R3 (first flower – beginning pod) stage. Symptoms don’t usually appear until the R4-R6 (full pod – full seed) growth stages. Foliar symptoms are interveinal coloring of grey-green and can resemble other soybean diseases such as brown stem rot or stem canker. Fluffy white mycelium growth can be found on the stems near the nodes. Leaves of infected plants eventually die but remain attached to the stem.

Areas to Watch

• Fields with a history of white mold will be at a higher risk for developing white mold again due to the increased inoculum. It is also important to note that the sclerotia (small, black overwintering structures) can persist in the soil for several years.
• Highly productive fields tend to produce excessive vegetative growth which restricts airflow through the canopy and therefore is more favorable for white mold.
• Narrow row spacing and high populations will also contribute to restricted airflow through the canopy and should be monitored.
• Fields planted to soybean varieties with low white mold tolerance are at a higher risk for developing white mold.

In-season Management

There are several products available that are considered “good” for controlling white mold. Some examples of these products are Aproach, Endura and Propulse fungicides. A new product that is looking very promising on white mold control is Viatude. Viatude combines picoxystrobin and prothioconazole, which are two effective modes of action. The rapid absorption and quick movement of Viatude helps to surround and protect the leaves and stems, resulting in increased effectiveness. Other options can be found on the Fungicide Efficacy Chart from Crop Protection Network at https://cropprotectionnetwork.s3.amazonaws.com/soybean-foliar-efficacy-2024.pdf.

Keep in mind that proper timing and proper application is crucial when using a fungicide for white mold control. The most effective fungicide timing is at R1 (first flower) but some affect can still be seen up to R3 (beginning pod). However, once white mold symptoms are apparent, fungicides will not be effective. Since timing is so critical, modeling tools like Sporecaster, have been developed to predict the apothecia (fruiting body that shoots spores) risk. Sporecaster is a free phone application that combines field information with research-based models to predict the best time for white mold treatment. If there is a risk factor above 40% during flowering, then a fungicide application should be considered.

Helpful Sprayer Tips

• Target mid to lower canopy
• Sprayer volumes of 15-20 GPA
• Slower application speeds, 10 MPH or less
• Spray pressure of 40 PSI or more
• Be sure to spray straight down into canopy

If you have any additional questions, please contact your Dairyland Seed Regional Agronomist.

Brian Weller
Western Region
507.456.3034

Rod Moran
Western Region
507.456.3034

Dan Ritter
Central Region
219.863.0583

Branden Furseth
Northern Region
608.513.4265

Mark Gibson
Eastern Region
260.330.8968

Amanda Goffnett
Eastern Region
989.400.3793

Ryan Mueller
Eastern Region
989.400.3793

Enjoying our Agronomy Updates? Suggestions for topics you'd like us to weigh in on? Drop us an email at dairylandseed@dairylandseed.com. We'd love to hear from you!